It is known in the prior art to hydroformylate olefins to produce aldehyde products in the presence of rhodium complex catalysts. The greatest body of the prior art deals with the hydroformylation of alpha olefins and internal olefins so as to produce a straight chain, terminally substituted aldehyde product instead of the iso- or branched chain aldehyde. Various prior art references do disclose the hydroformylation of internal olefins to produce branched chain aldehydes; however these prior art processes are not generally economically feasible because of extreme conditions of heat and pressure required, or because of low conversions or selectivities. Also, many prior art processes utilize catalysts which, while they initially produce good results, slowly degrade and become unstable in a continuous process as is normally used in commercial production. Thus "batch runs" do not always provide a proper catalyst evaluation since catalyst stability cannot be properly evaluated except in a continuous process. Further, the prior art references do not disclose a manner by which one can predict whether a particular catalyst will give good results in the production of a branched chain aldehyde.
Even though most of prior art deals with the production of a straight chain, terminally substituted aldehyde product, in many instances the branched chain aldehyde is desired. For example, branched chain aldehydes, as opposed to the straight chain isomers, are desirable as starting materials for the production of many polymer products. Thus, 2-methylbutanal, which may be produced from butene-2, is useful as the starting material for the production of isoprene.
It is thus an object of the present invention to provide a process for the hydroformylation of butene-2 to produce 2-methylbutanal with high selectivity. It is also an object of the present invention to provide a process for the hydroformylation of butene-2 to produce 2-methylbutanal under economically feasible process conditions and at high reaction rates and selectivities, and which utilizes a catalyst with good stability under continuous operating conditions. It is also an object of the present invention to provide a method by which one may predict whether or not a particular catalyst will be effective for hydroformylation of butene-2 to 2-methylbutanal, and the parameters for such a catalyst. These and other objects of the present invention will become apparent from the following description of the present invention.